Soldering method, component to be joined by the soldering method, and joining structure

ABSTRACT

It is possible to prevent deterioration of a soldering portion and improve strength of thermal fatigue resistance by providing barrier metal layers on at least one of lead and land to cover parent materials comprising Cu-containing materials, feeding a soldering material between the lead and the land and allowing to contact in a fused condition with barrier metal layers and solidify, and thus soldering together the lead and the land.

[0001] The present application is based on Japanese Patent ApplicationNo. 2003-028032, which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a method for soldering onemember to another member, and more specifically to a method forsoldering a land formed on a board and an electrode of electroniccomponent (e.g., lead) in a process of manufacturing an electroniccircuit board. Furthermore, the invention relates to a joining structureobtained by this soldering method and an electrical component or anelectronic component used in this soldering method.

[0004] 2. Description of the Related Art

[0005] In processes for manufacturing an electronic circuit board usedfor the electronic equipment, the method of reflow soldering hashitherto been known as one of methods used for mounting an electroniccomponent on a board, more specifically for joining electrically andphysically a lead pulled out of the electronic component to a landformed on the board.

[0006] In a general method of reflow soldering, at first, a so-calledcream solder (not shown in drawings) is provided by screen printing on aland that is part of a wiring pattern formed on the board. The creamsolder in general is made by mixing a solder powder comprising asoldering material with a flux comprising rosin, activating agent, andsolvent. Thereafter, an electronic component is set on a prescribedportion of a board so that a lead pulled out of the electronic componentadheres to the cream solder set on the land to be joined. The flux isactivated by a thermal treatment of the board on which the electroniccomponent is thus set through the cream solder at a temperature higherthan the melting point of the soldering material used, thus a solderingmaterial forming the solder powder in the cream solder is once fused,and simultaneously other components such as the flux in the cream solderis allowed to evaporate (or volatilize). Subsequently, the solderingmaterial fused is solidified by cooling (or standing for cooling) Thesolidified soldering material forms a joining portion between the leadof the electronic component and the land of the board to join themelectrically and physically. Although other components than thesoldering material such as the flux can exist in the joining portion,these other components causes phase separation from the solderingmaterial at the thermal treatment, fail to exist inside the joiningportion, and only remain slightly on the surface of the portion. Thus,an electronic circuit board having the electronic component mounted onthe board by the joining portion (or soldering portion) comprising thesoldering material substantially is obtained.

[0007] Soldering materials used generally include Sn—Pb seriesmaterials, particularly that having an eutectic composition (Hereinaftersimply referred to as a Sn—Pb eutectic material). It is known that theeutectic composition of the Sn—Pb series material is a Sn—37Pbcomposition (i.e., a composition consisting of 37 weight percent of Pband the residual Sn (of 63 weight percent)), and the Sn—Pb seriesmaterial has a melting point of 183° C. in this eutectic composition.For example, see Unexamined Japanese Patent Publication No. 2000-260801.

[0008] In recent years, the waste disposal of electronic equipmenthaving the above-described electronic circuit board have offered aproblem, and effects on the global environment and the human bodyexerted by the lead (Pb) contained in soldering materials have become amatter of concern. Therefore, there's movement toward use of materialscontaining no lead, that is, lead-free soldering materials as solderingmaterials in place of the Sn—Pb series materials used so far, and thepractical use thereof has been attempted.

[0009] Recently, materials having various compositions have beenproposed as the lead-free soldering materials and one of such materialsis a Sn—Zn series material. As a result of recent studies, it was foundthat the Sn—Zn series material had an eutectic composition of aboutSn—9Zn (i.e., nine weight percent of Zn and the residual Sn (91 weightpercent)) and the Sn—Zn series material had a melting point of 199° C.in the eutectic composition.

[0010] It is desirable that the melting point of the lead-free solderingmaterials are sufficiently low to the extent that the electroniccomponent is not damaged and is comparatively near to the melting pointof the conventional Sn—Pb series materials in consideration of theheat-resistant temperature of the electronic component to be mounted ona board and the application of an existing soldering method. Since themelting points of the above-described Sn—Zn series materials are lowerthan those of other lead-free soldering materials such as Sn—Ag seriesmaterials and comparatively near to those of the Sn—Pb series materials,the Sn—Zn series materials are expected as leading substitutes for theSn—Pb series materials.

[0011] Although use of the Sn—Zn series materials in place of the Sn—Pbseries materials had an advantage of soldering an electronic componentto a board without causing thermal damage to the electronic component,however, it was found that the joining portion between the land of theboard and the lead of the electronic component was deteriorated and nosufficient strength of thermal fatigue resistance was obtained as aresult of the continuous use test of the resulting electronic circuitboard under a condition of high temperature.

[0012] This is thought to be caused by contact of lead (Zn) contained inthe Sn—Zn series materials with copper (Cu) used as a material of theland and the lead and forming an intermetallic compound comprising Cuand Zn at the joining interfaces between the joining portion and theland and between the joining portion and the lead.

[0013] An electronic circuit board prepared by soldering an electroniccomponent and a board by use of a cream solder containing cream powdercomprising the Sn—Zn series material in place of the Sn—Pb seriesmaterial according to the above-described conventional method of reflowsoldering is hereinafter illustrated through FIG. 2.

[0014] In this electronic circuit board, a land 7 formed on a board 6and a lead 9 pulled out of an electronic component 10 are joinedelectrically and mechanically. The land 7 in general is made of Cu andformed in one united body with a wiring pattern. Furthermore, the lead 9in general is prepared by covering a parent material 9 a made of Cu witha plating 9 b comprising a Sn—Pb eutectic material. A joining portion 8is formed by a thermal treatment of the cream solder, and formedsubstantially of a soldering material stemming from the solder powder asdescribed above.

[0015] Although freedom from lead is promoted also as to a solderingmaterial for the lead of an electronic component at present, the Sn—Pbseries materials are still used nowadays as a transition period in somecases.

[0016] Since the soldering material directly contacts with the land 7 inthe thermal treatment, Cu forming the land diffuses into the solderingmaterial and combines with Zn to form an intermetallic compound 11comprising Cu and Zn at this joining interface.

[0017] Furthermore, as the soldering material of solder powder fuses inthe thermal treatment, the plating 9 b consisting of a Sn—Pb eutecticmaterial having a melting point lower than the temperature of thethermal treatment also fuses, the portion of the plating 9 b contactingwith the soldering material in a fused condition fuses and diffuses intothe soldering material. Consequently, the plating 9 b of the lead 9 ispeeled off at places and the parent material 9 a comes to contactdirectly with the soldering material in the fused condition.Accordingly, the Cu composing the parent material 9 a of the lead 9diffuses into the soldering material similarly as described above andcombines with Zn to form an intermetallic compound 12 comprising Cu andZn at the joining interface.

[0018] When the board having the electronic component soldered asdescribed above are placed particularly under a condition of hightemperature for a long period of time, more much Cu diffuses into thejoining portion (or the soldering material) to promote the formation ofthe intermetallic compounds 11 and 12 comprising Cu and Zn. All Zn inthe soldering material is soon consumed for the formation of theintermetallic compound comprising Cu and Zn, subsequently Cu remainingwithout contributing to the formation of the intermetallic compoundand/or Cu composing the Cu—Zn intermetallic compound diffuse into thesoldering material, and spreading diffusion of Sn in the solderingmaterial into voids produced by the diffusion of the Cu, that is,interdiffusion occurs. This phenomenon is thought to invite thedeterioration of the joining portion.

[0019] Also, in the case where a cream solder containing the solderpowder comprising the Sn—Pb series material is conventionally used, thecopper (Cu) used as a material for the land and/or the lead diffusesinto the joining portion and combines with tin (Sn) contained in theSn—Pb series material, and thereby the intermetallic compound comprisingSn and Cu can be formed between the joining interfaces and the landand/or the lead at the joining portion. However, since the intermetalliccompound comprising Sn and Cu is stable, the compound can endurecontinuous use under a condition of high temperature. Accordingly, theformation of the intermetallic compound comprising Sn and Cu is thoughtto invite no problem of deterioration of the joining portion that occursin the case of the intermetallic compound comprising Cu and Zn.

[0020] Furthermore, a Fe—42Ni alloy material (i.e., an alloy materialhaving a composition comprising 42 weight percent of Ni and the residualFe (58 weight percent)) is used in some cases as the material for theparent material 9 a of the lead 9 as well as Cu. In this case, theintermetallic compound 12 comprising Cu and Zn is not formed at theinterface between the lead 9 and the joining portion 8 by allowing theplating 9 b on the lead 9 to fuse and diffuse into the solderingmaterial and allowing the parent material 9 a to contact directly withthe soldering material. However, since the intermetallic compound 12comprising Cu and Zn is still formed at the interface between the land 7comprising Cu and the joining portion 8, deterioration of the joiningportion occurs when the resulting electronic circuit board is subjectedto a continuous use test under a condition of high temperature.Accordingly, this alloy material also has the problem of having nosufficient strength of thermal fatigue resistance.

[0021] Although the Sn—Zn series material has been described above indetail, other soldering materials containing at least Sn and Zn alsoencounters similar problems.

SUMMARY OF THE INVENTION

[0022] The object of the invention is to provide a soldering method thatcan prevent deterioration of the soldering portion (or joining portion)caused by continuous use under a condition of high temperature and canobtain a sufficient strength of thermal fatigue resistance, which is aproblem inherent in the case where soldering (or joining) of anelectronic component and a board is carried out by use of the solderingmaterials containing Sn and Zn such as the Sn—Zn series material, and anelectronic circuit board obtained by this method.

[0023] According to one of the points of the present invention, theinvention provides a method for soldering (or joining. The same shallapply hereinafter.) the first member and the second member by use of asoldering material containing Sn and Zn such as the Sn—Zn seriesmaterial, wherein a barrier metal layer to cover a parent materialcomprising a Cu-containing material is provided on at least one of thefirst member and the second member, a soldering material is fed (or set)between the first member and the second member and allowed to contactwith the barrier metal layer in a fused condition and solidify.

[0024] According to the above-described soldering method, since theparent material comprising a Cu-containing material is covered with thebarrier metal layer and the soldering material containing Sn and Zncontacts with the barrier metal layer, direct contact of the Zn of thesoldering material with the Cu contained in the parent material can beevaded. This enables an effective inhibition or prevention of theformation of an intermetallic compound comprising Cu and Zn, and therebythe cause of deterioration of a soldering portion (also referred to as ajoining portion in this specification) caused by continuous use under acondition of high temperature and furthermore the cause of reduction instrength of thermal fatigue resistance can be excluded.

[0025] When both of the first member and the second member are made ofthe Cu-containing material and Cu can diffuse from both members into thesoldering material (or the joining portion) in the invention, it ispreferable that the Cu-containing material is covered with the barriermetal layer to evade direct contact with the soldering material, therebyto prevent the formation of the intermetallic compound comprising Cu andZn. However, the invention is not necessarily limited to this and evenin the above-described case, deterioration in strength of thermalfatigue resistance can be reduced by providing the barrier metal layerfor either of both members as compared with the case where no barriermetal layer is provided at all.

[0026] Although the barrier metal layer may be formed of either of amonolayer and multilayer in the invention, it is necessary to cover theparent material containing Cu so that the parent material does notsubstantially contact with the soldering material in a fused condition.Accordingly, materials of the barrier metal layer used preferablyinclude those that do not substantially diffuse (dissolve) into thesoldering material in a fused condition or do not substantially contactwith the soldering material by exposure of the parent materialcontaining Cu positioned in the lower portion thereof even if thematerials diffuses. In the present specification, on the basis of theparent material of the member to be soldered, the exposed surface sideto contact with the soldering material is referred to as the “upside”whereas the side of the parent material is referred to as the“downside”.

[0027] In a preferred embodiment of the invention, the barrier metallayer can be a Ni layer (i.e., a layer made of Ni, other layers asdescribed later are similar to this manner) or a multilayer laminate.Since Ni hardly diffuse into a soldering material by contacting with thesoldering material and the parent material positioned on downside of itis not exposed, the Ni is suitable as a material for the barrier metallayer.

[0028] When a multilayer laminate containing a Ni layer is used as thebarrier metal layer, an Au layer can be provided on the upside of the Nilayer. The Ni layer is subject to oxidation in the air and comparativelyinferior in wettability to the soldering material because of formationof the oxide. However, when the Au layer is provided on the upside ofthe Ni layer, the Au layer is more resistant to oxidation than the Nilayer and shows a good wettability to the soldering material. Byproviding this layer on the upside of the Ni layer to form the surfaceof the barrier metal layer, the wettability to the soldering materialcan be improved as compared with use of the single Ni layer as thebarrier metal layer and thereby the reliability to joining of thejoining portion (mainly, bonding strength) can be improved.

[0029] The layer composing the barrier metal layer (at least one layerwhen the barrier metal layer is a multilayer laminate) can be formed bymethods known in this technical field, for example, electroplating,hot-dip plating, immersion plating, vapor deposition, and the like.

[0030] According to another point of the invention, a joining structurehaving the first member and the second member soldered by use of asoldering material containing Sn and Zn wherein at least one of thefirst member and the second member is equipped with a parent materialcomprising a Cu-containing material and a barrier metal layer coveringthe parent material is provided.

[0031] Since the parent material comprising a Cu-containing material iscovered with the barrier metal layer also in this joining structure, theformation of the intermetallic compound comprising Cu and Zn iseffectively inhibited or prevented similarly to the above-describedsoldering method of the invention. Consequently, the joining structurecan maintain a high strength of thermal fatigue resistance withoutcausing deterioration of the joining portion in the continuous use undera condition of high temperature.

[0032] Although the barrier metal layer of the joining structureprepared by the soldering method of the invention leaves the Ni layer,when the Ni layer and the Au layer positioned on the upside of the Nilayer are used, the Au and Zn are allowed to react on the upside of theNi layer and to form an Au—Zn compound in a layer state without elution(or fusion diffusion) of the Au into the soldering material caused bycontact of the Au layer with the soldering material in a fusedcondition, thus it is possible to obtain a higher adhesive power and ahigher strength of thermal fatigue resistance than the single Ni layer.

[0033] In the invention, the first member and the second member can be aboard and an electronic component and in more detail, can be anelectrode provided on the board and an electrode of electroniccomponent, respectively.

[0034] The above-described board includes those made of paper phenolicmaterials, glass epoxy materials, polyimide film materials, ceramicmaterials, and metallic materials, and the like. The electrode formed onsuch board can be, for example, a land formed in one united body with awiring pattern and can be prepared, for example, by covering the parentmaterial comprising Cu with the barrier metal layer.

[0035] The electronic component as described above includessemiconductor components (e.g., so-called QFP (Quad Flat Package)component, CSP (Chip Scale Package) component, and SOP (Single OutsidePackage) component, etc.), chip components (e.g., resistance, condenser,transistor, inductor), and connectors and the like. These electrodes ofelectronic components can be, for example, leads or terminals pulled outof electronic components and can be prepared, for example, by covering aparent material comprising Cu with a barrier metal layer.

[0036] However, the invention is not limited by these members, and thefirst member and the second member can be various members to be solderedup. Accordingly, according to further another point of the invention, anelectrical component or an electronic component having an electrodeequipped with a parent material comprising a Cu-containing material anda barrier metal layer covering the parent material, which is to besoldered by use of a soldering material containing Sn and Zn also, canbe provided.

[0037] In this specification, the soldering material means a metallicmaterial having a comparative low melting point, that is, a metallicmaterial that fuses at temperature of about 100 to about 250° C. Ofthese soldering materials, the soldering materials containing Sn and Znare those containing at least Sn and Zn, for example, can be Sn—Znseries materials (containing Sn—Zn eutectic material and Sn—Zn—Bimaterials to which Bi is added to the Sn—Zn eutectic material).Furthermore, an “A-B series material” means a material that further cancontain a trace of another metallic component on a basis of eutecticcomposition comprising metallic components A and B. For example, theSn—Zn series materials can contain a trace amount of another metalliccomponent (It is not important whether the another metallic component isintentionally added or inevitably contained) in addition to the eutecticcomposition of Sn—9Zn. The Sn—Zn series materials can have a meltingpoint between about 190 and about 200° C.

[0038] The skilled person in the art will readily understand that in theinvention, for example, soldering can be carried out by any of thereflow soldering method and flow soldering method, and any of solderingof only one side of a board and soldering of both sides thereof also canbe carried out, and furthermore the joining structure of the inventioncan be prepared by any of these methods.

[0039] The concept of preventing the contact of Cu with Zn by providinga barrier metal layer in the invention will be appropriately utilizedwhen abuses due to formation of the intermetallic compound comprising Cuand Zn that coexist are desired to be excluded.

[0040] The soldering method in the invention can be understood also asthe method for preparing the joining structure where the first memberand the second member are soldered.

BRIEF DESCRIPTION OF THE DRAWINGS

[0041]FIG. 1 shows a schematic partial sectional view of an electroniccircuit board prepared by a soldering method in one mode for carryingout this invention; and

[0042]FIG. 2 shows a schematic partial sectional view of an electroniccircuit board prepared by a conventional soldering method.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0043] One mode for execution is hereinafter illustrated through FIG. 1.FIG. 1 is a schematic partial sectional view of an electronic circuitboard prepared by the soldering method in this mode for execution.

[0044] First, a board 1 and electronic component 5 to be joined theretoare prepared. A land 2 prepared by covering a parent material 2 acomprising Cu with a barrier metal layer 2 b comprising a Ni layer andan Au layer is formed on the board 1, and the land 2 can be formed, forexample, according to the following method.

[0045] For example, the parent material 2 a comprising Cu is formed inone united body with a wiring pattern (not shown in the figure) on theupper surface of the board 1 made of a glass epoxy resin or the like bythermo-compression bonding (or mounting) of copper foil and etching. Thewiring pattern can have a width of, for example, about 50 to about 100μm. Thereafter, a resist is formed in a prescribed region of the surfaceof the board 1 to cover the wiring pattern. Then, the parent material 2a is exposed without being covered with the resist. The height of theparent material 2 a (i.e., the height of the wiring pattern) isadjusted, for example, to about 10 to about 40 μm.

[0046] A Ni layer is formed by immersing the board 1 on which the parentmaterial 2 a is thus formed in an electrolyte having Ni dissolved andapplying an appropriate voltage to the parent material 2 a to deposit Nion the surface of the parent material 2 a by the use of electrolessplating. The height of the Ni layer can be adjusted, for example, toabout 2 to about 5 μm. Furthermore, if a gold plate is formed, forexample, so as to be from 0.01 μm to 0.1 μm on the Ni surface byimmersion plating, the land 2 comprising the parent material 2 a and thebarrier metal layer 2 b (in this mode for execution, Ni/Au layer)covering the parent material can be formed on the surface of the board1. Looking at the board 1 from above, the land 2 has a rectangularoutline and can be, for example, about 0.5 to about 2 mm in width andabout 0.5 to about 2 mm in length, but in this mode for execution, theland can have an arbitrary suitable shape and size without limitation asdescribed above.

[0047] Although the method for forming the Ni layer by electroplatingwas shown in this mode for execution, in addition to this method, the Nilayer covering the parent material 2 a can be formed, for example, byhot-dip plating where the board 1 having the parent material 2 a formedis dipped into a Ni material in a fused condition, immersion platingwhere this board is immersed in a solution containing a metal forplating to substitute the surface of the parent material 2 a with ametal for plating, or vapor deposition where Ni is evaporated anddeposited on the parent material 2 a. The person skilled in the art willbe able to carry out the electroplating, hot-dip plating, and vapordeposition by setting suitable conditions.

[0048] On the other hand, a lead 4 is provided on electronic component5. The lead is prepared by covering a parent material 4 a made of Cuwith a barrier metal layer 4 b formed of a Ni monolayer. This lead canbe prepared beforehand by forming a Ni layer on the surface of theparent material 4 a as the barrier metal layer 4 b according to themethod as described above, and electronic component 5 can be prepared byuse of this lead.

[0049] A cream solder is provided on the land 2 of the board 1 preparedas described above, for example, by screen printing or a dispenser. Thiscream solder is prepared by dispersing a Sn—Zn series material, forexample, a metallic particle (or solder powder) consisting of a Sn—Zneutectic material into flux. Commercial available flux comprising rosin,an activator, and solvent can be used as the flux. The metallic particlecan have an average particle size of, for example, about 20 to about 40μm and can exist in a ratio of about 85 to about 90 weight percent tothe total cream solder.

[0050] Then, the electronic component 5 is appropriately set on theboard 1 so that the lead 4 of the electronic component contacts with thecream solder supplied on the land 2. Herein, the cream solder contactswith the barrier metal layer 4 b of the lead 4 and the barrier metallayer 2 b of the land 2 and fails to contact parent materials 4 a and 2a. The board 1 thus prepared is subjected to a thermal treatment byallowing it to pass through a hot atmosphere of, for example, from about205 to about 230° C., and preferably from about 210 to about 220° C. Bythis treatment, heat is supplied to the cream solder, the Sn—Zn seriesmaterial forming the metallic particle in the cream solder is fused, andsimultaneously other components than the metallic particle in the fluxis evaporated (or vaporized) and removed.

[0051] The Sn—Zn series material in a fused condition contacts with thebarrier metal layers 2 b and 4 b, but fails to contact directly withparent materials 2 a and 4 a because Ni forming these layers does notnearly fuse and diffuse. Accordingly, formation of the intermetalliccompound comprising Cu and Zn is prevented. Then, in order to form theAu—Zn compound layer in a layer state by reacting Au positioned on theupside of Ni reacts with Zn in the solder and in order to improve theadhesion to solder, the soldering must be carried out at temperature offrom about 205 to about 230° C. and preferably from about 210 to about220° C. Temperature higher than the above-described temperature allow Auand Zn to react and fuse in the solder without forming a compound in alayer state, and thereafter form a granular Au—Zn compound. Intemperature lower than the above-described temperature, Au and Zn failto react sufficiently. The thickness of the Au—Zn compound layer ispreferably from 0.01 to 0.1 μm. Exceeding this range of thickness causesfragileness in joining property of the Au—Zn layer and contrarily, whena thickness does not reach this range, the effect hardly is obtained.

[0052] Subsequently, the board 1 having undergone the thermal treatmentis cooled (or stand for cooling) to solidify the Sn—Zn series materialin a fused condition, thus forming a joining portion (or solderingportion) 3 comprising substantially the Sn—Zn series material. The lead4 of an electronic component 5 and the land 2 of the board 1 areelectrically and mechanically joined (or soldered) through the joiningportion 3.

[0053] According to the above-described process, an electronic circuitboard mounting where the electronic component 5 is mounted on the board1 is prepared. The formation of the intermetallic compound comprising Cuand Zn can be prevented in any of the joining interface between the lead4 of the electronic component 5 and the joining portion 3 and thejoining interface between the land 2 of the board 1 and the joiningportion 3 in the resulting electronic circuit board.

[0054] Although the inventors supposed in this mode for execution thatboth parent materials of the land and the lead comprise Cu and arecovered with the respective barrier metal layers, the invention is notlimited to this and it is sufficient that at least one of both parentmaterials contains Cu and the parent material containing Cu is coveredwith a barrier metal layer. For example, when the parent material of alead comprises a Fe—42Ni alloy material and contains no Cu, it is notalways necessary to cover the parent material with a barrier metal layerand it is enough just to cover the parent material with a soldercomprising, for example, a Sn—Pb series material or the like.

[0055] According to the present invention, in the method of solderingthe first member and the second member by use of a soldering materialcontaining Sn and Zn, at least one of the first member and the secondmember has a portion comprising a Cu-containing material as a parentmaterial, a barrier metal layer covering the parent material isprovided, a soldering material in a fused condition is allowed tocontact with the barrier metal layer and solidify, thus to solder (orjoin) the first member and the second member.

[0056] According to this soldering method, the Zn in the solderingmaterial fails to directly contact with the Cu contained in the parentmaterial, and thereby the formation of the intermetallic compoundcomprising Cu and Zn can be effectively inhibited or prevented, thus toexpel deterioration of the joining portion due to continuous use under acondition of high temperature and furthermore the cause invitingdeterioration in strength of thermal fatigue resistance.

[0057] In addition, according to the invention, in a joining structurewhere the first member and the second member are soldered by use of asoldering material containing Sn and Zn, at least one of the firstmember and the second member is equipped with the parent materialcomprising a Cu-containing material and a barrier metal layer coveringthe parent material, and accordingly the same effect as described abovecan be obtained.

[0058] Although the invention has been described in its preferred formwith a certain degree of particularity, it is understood that thepresent disclosure of the preferred form can be changed in the detailsof construction and in the combination and arrangement of parts withoutdeparting from the spirit and the scope of the invention as hereinafterclaimed.

What is claimed is:
 1. A method of soldering a first member and a secondmember by use of a soldering material containing Sn and Zn, comprisingsteps of: providing a barrier metal layer covering a parent materialmade of a Cu-containing material on at least one of the first member andthe second member; feeding the soldering material between the firstmember and the second member; contacting the soldering material in afused condition with the barrier metal layer; and solidifying thesoldering material to thereby solder the first member and the secondmember.
 2. A method according to claim 1, wherein the barrier metallayer contains a Ni layer.
 3. A method according to claim 2, wherein thebarrier metal layer further contains an Au layer that is positioned on aside far from the parent material.
 4. A method according to claim 1,wherein at least one layer of the barrier metal layer is formed by amethod selected from the group consisting of electroplating, hot-dipplating, immersion plating, and vapor deposition.
 5. A method accordingto claim 1, wherein the first member is an electrode formed on a boardand the second member is an electrode of electronic component.
 6. Amethod according to claim 1, wherein the soldering material is kept in afused condition at a temperature of 205 to 230° C. and then the firstmember and the second member are soldered.
 7. A joining structureprepared by soldering a first member and a second member by use of asoldering material containing Sn and Zn, wherein at least one of thefirst member and the second member has a parent material comprising aCu-containing material and a barrier metal layer covering the parentmaterial.
 8. A joining structure according to claim 7, wherein thebarrier metal layer further contains an Au—Zn compound layer that ispositioned on a side far from the parent material.
 9. A joiningstructure according to claim 8, wherein the thickness of the Au—Zncompound layer is from 0.01 to 0.1 μm.
 10. A joining structure accordingto claim 7, wherein the first member is an electrode formed on a boardand the second member is an electrode of electronic component.
 11. Anelectrical or electronic component to be soldered by use of a solderingmaterial containing Sn and Zn, said component having an electrodecomprising a parent material comprising a Cu-containing material and abarrier metal layer covering the parent material.